This project is directed toward a molecular understanding of the enhancer elements and the trans-acting transcriptional factors that interact with enhancers. A recent focus of this project has been the role of the 3' long open reading frame of the human T-cell leukemia virus type-I (HTLV-I) which encodes a 40-Kd protein (p40x) that positively regulates transcription directed by the HTLV-I long terminal repeat (LTR) in a phenomenon known as trans-activation. We have succeeded in expressing the complete p40x coding sequence in E. coli and in baculovirus vector as a 40-Kd protein. Both p40x proteins are capable of stimulating transcription from HTLV-I LTR. Significant purification of the p40x proteins has been achieved. Our future objective is to understand the biochemical mechanism of trans-activation by the p40X protein and the involvement of cellular transcription factors in this process.